The Cherries identified Silva as a suitable replacement for Marcos Senesi, who left to join Premier League rivals Tottenham upon the expiry of his contract at the end of last season.
Silva completed his medical this week and has been unveiled by Bournemouth in what is an impressive summer move as they snap up the 22-year-old who captained Benfica in both legs of their UEFA Europa League qualifier against St. Gallen last month.
Speaking on the move to the English top flight, Silva said he cannot wait to get the pitch ahead of the new season which begins in 3 weeks time.
"I am very happy to be here. It's a pleasure to play for Bournemouth and in the Premier League. I can't wait to start the season with my teammates and I'm excited to be here.
"The mentality is always to win. I will try my best, and I will play for the fans. We have everything here that helps us perform on the pitch, and I can't wait to get started."
Silva has made 235 senior appearances for the Portuguese giants and has made 20 international appearances for Portugal, featuring in the 2022 Qatar World Cup at the age of 19.
Under Marco Rose, Bournemouth are rebuilding a defence that has lost the likes of Illia Zabarnyi, Milos Kerkez, Marcos Senesi and Dean Huijsen in recent years.